Battery pack

ABSTRACT

A battery pack includes: a plurality of secondary battery cells connected to each other in series and/or in parallel; and a housing case that includes a plurality of battery housing spaces for housing the plurality of secondary battery cells. A number of the plurality of battery housing spaces is larger than a number of the plurality of secondary battery cells. A heat absorber is disposed in the battery housing space where the secondary battery cell is not housed.

TECHNICAL FIELD

The present invention relates to a battery pack.

BACKGROUND ART

A battery pack which houses a plurality of cylindrical secondary battery cells in a housing case is used as a power source for an electronic device such as a laptop computer and a portable electronic terminal. This battery pack connects the plurality of cylindrical secondary battery cells in series or in parallel to increase a capacity of the battery pack. Particularly in recent years, it has been demanded to increase the capacity of the battery pack, and also to reduce a size and a weight of the battery pack in terms of portability or the like of the battery pack. Accordingly, it has been promoted to increase each capacity of the secondary battery cells. Moreover, it has been adopted to arrange the secondary battery cells without gaps between the respective secondary battery cells inside the battery pack.

Meanwhile, the secondary battery cells may cause thermal runaway for various reasons such as internal short circuit and overcharge. When any one of a plurality of the secondary battery cells located adjacent to each other causes thermal runaway, the adjacent secondary battery cell is heated and further induces thermal runaway. This thermal runaway propagates and may cause thermal runaway of a large number of the secondary battery cells. It is therefore demanded to eliminate an effect of thermal runaway on the other secondary battery cells even if any one of the secondary battery cells causes thermal runaway.

CITATION LIST Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. 6-80260

PTL 2: Unexamined Japanese Patent Publication No. 2014-86342

SUMMARY OF THE INVENTION

The present invention has been developed in view of these circumstances. One of objects of the present invention is to provide a battery pack capable of avoiding a chain of thermal runaway while using a plurality of secondary battery cells.

A battery pack of an aspect of the present invention is a battery pack including: a plurality of secondary battery cells connected to each other in series and/or in parallel; and a housing case that includes a plurality of battery housing spaces for housing the plurality of secondary battery cells. A number of the plurality of battery housing spaces may be larger than a number of the plurality of secondary battery cells. A heat absorber may be disposed in the battery housing space where the secondary battery cell is not housed. According to this configuration, the heat absorber absorbs generated heat to reduce a chain of thermal runaway even if any one of the secondary battery cells causes thermal runaway. Moreover, the use of the battery housing space where the secondary battery cell is not housed contributes to effective utilization of a limited space inside the housing case, and prevention of a size increase of the battery pack.

In addition, according to a battery pack of another aspect of the present invention, in addition to the above configuration, each of the secondary battery cells may have a cylindrical exterior can.

Furthermore, according to a battery pack of a further aspect of the present invention, in addition to any one of the above configurations, the heat absorber may be a metal part that has a columnar shape hollow inside. This shape increases a surface area and enhances a heat absorption effect while reducing a weight of the heat absorber.

In addition, according to a battery pack of a still further aspect of the present invention, in addition to any of the above configurations, the heat absorber may have a length smaller than a length of each of the secondary battery cells. According to this configuration, the heat absorption effect can be produced while reducing a required volume for weight reduction.

Moreover, according to a battery pack of a still further aspect of the present invention, in addition to any one of the above configurations, the heat absorber may be eccentrically disposed in the battery housing space on a side close to the different battery housing space where the secondary battery cell is housed, the different battery housing space being adjacent in a longitudinal direction of the battery housing space. According to this configuration, by disposition close to the end surface of the secondary battery cell corresponding to a heat absorbing target, the heat absorption effect can be effectively exerted during heat generation from the corresponding secondary battery cell.

Furthermore, according to a battery pack of a still further aspect of the present invention, in addition to any one of the above configurations, the heat absorber may be made of aluminum. According to this configuration, stable characteristics including excellent heat transfer without corrosion or the like can be exhibited.

Moreover, in addition to any one of the above configurations, a battery pack of a still further aspect of the present invention may further include: a longitudinal partition plate that extends in a longitudinal direction of the housing case; and partitions an interior of the housing case in a lateral direction orthogonal to the longitudinal direction to section the plurality of battery housing spaces.

Furthermore, in addition to any one of the above configurations, a battery pack of a still further aspect of the present invention may further include a lateral partition plate that crosses the longitudinal partition plate, and constitutes the plurality of battery housing spaces.

In addition, according to a battery pack of a still further aspect of the present invention, in addition to any of the above configurations, side surfaces of the plurality of secondary battery cells may be covered by insulating thermal resistant plates. Each of the insulating thermal resistant plates may be curved around a position where the adjacent secondary battery cells come closest to each other in a cross-sectional view. According to this configuration, a flame exhaust direction can be regulated in such a manner that flame exhaust does not flow toward the side surface of the different adjacent secondary battery cell when flame is exhausted from the side surface as a result of thermal runaway of one of the secondary battery cells. Accordingly, safety improves.

In addition, according to a battery pack of a still further aspect of the present invention, in addition to any of the above configurations, the insulating thermal resistant plate may be made of mica. According to this configuration, cost reduction and high thermal resistance are achievable.

Advantageous Effect of Invention

According to the battery pack of the present invention, the heat absorber absorbs generated heat to reduce a chain of thermal runaway even if any one of the secondary battery cells causes thermal runaway. Moreover, the use of the battery housing space where the secondary battery cell is not housed contributes to effective utilization of a limited space inside the housing case, and prevention of a size increase of the battery pack.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a battery pack according to a first exemplary embodiment.

FIG. 2 is a perspective view of the battery pack of FIG. 1 as viewed obliquely from below.

FIG. 3 is a cross-sectional view of the battery pack of FIG. 1 taken along line III-III.

FIG. 4 is a plan view of the battery pack of FIG. 1.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4.

FIG. 6 is an enlarged cross-sectional view of FIG. 5.

FIG. 7 is an exploded perspective view showing a state of the battery pack of FIG. 4 from which a cover is removed.

FIG. 8 is a plan view of the battery pack of FIG. 7.

FIG. 9 is an exploded perspective view of the battery pack of FIG. 4.

FIG. 10 is an exploded perspective view showing a state of the battery pack of FIG. 8 from which a longitudinal partition plate and lateral partition plates are removed.

FIG. 11 is an exploded perspective view showing a state the battery pack of FIG. 10 from which insulating thermal resistant plates, secondary battery cells, and heat absorbers are disassembled.

FIG. 12 is a schematic cross-sectional view showing a flame exhausting path of a battery pack according to Comparative Example 1.

FIG. 13A is a schematic cross-sectional view showing a flame exhausting path of a battery pack according to Comparative Example 2, and FIG. 13B is a schematic cross-sectional view showing a flame exhausting path of the battery pack according to the first exemplary embodiment.

FIG. 14 is an enlarged cross-sectional view showing the longitudinal partition plate of the battery pack according to the first exemplary embodiment.

FIG. 15 is an enlarged cross-sectional view showing a longitudinal partition plate of a battery pack according to Comparative Example 3.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will be hereinafter described with reference to the drawings. Note that the exemplary embodiments described hereinafter are presented as examples embodying a technical idea of the present invention. Accordingly, the present invention is not limited to the followings. In addition, the present description is not definitely presented to limit parts described in the claims to corresponding parts described in the exemplary embodiments. Unless otherwise specified, dimensions, materials, shapes, relative positions, and the like of constituent parts described in the exemplary embodiments are only presented as explanatory examples, and are not intended to limit the scope of the present invention. Note that sizes, positional relationships, and the like of parts shown in the respective drawings may be exaggerated for clarifying the explanation. Furthermore, identical names and reference numerals indicate identical or similar parts in the following description, and detailed description will be omitted where appropriate. In addition, concerning respective elements constituting the present invention, a plurality of elements may be constituted by an identical part such that one part functions as a plurality of elements, or conversely, a function of one part may be shared and implemented by a plurality of parts.

First Exemplary Embodiment

Each of FIGS. 1 to 11 shows a battery pack according to a first exemplary embodiment of the present invention. In these figures, FIG. 1 is a perspective view showing battery pack 100 according to the first exemplary embodiment, FIG. 2 is a perspective view of battery pack 100 of FIG. 1 as obliquely viewed from below, FIG. 3 is a cross-sectional view of battery pack 100 of FIG. 1 taken along line III-III, FIG. 4 is a plan view of battery pack 100 of FIG. 1, FIG. 5 is a cross-sectional view taken along line V-V of FIG. 4, FIG. 6 is an enlarged cross-sectional view of FIG. 5, FIG. 7 is an exploded perspective view showing a state of the battery pack of FIG. 4 from which a cover is removed, FIG. 8 is a plan view of the battery pack of FIG. 7, FIG. 9 is an exploded perspective view of FIG. 4, FIG. 10 is an exploded perspective view showing a state of the battery pack of FIG. 8 from which a longitudinal partition plate and lateral partition plates are removed, and FIG. 11 is an exploded perspective view showing a state of the battery pack of FIG. 10 from which insulating thermal resistant plates, secondary battery cells, and heat absorbers are disassembled. Battery pack 100 houses a plurality of secondary battery cells 1 inside, and connects secondary battery cells 100 in series or in parallel to achieve a capacity increase and allow charging and discharging. Power is supplied by connecting battery pack 100 to an external device corresponding to a driving target, and discharging secondary battery cells 1. Presented herein is an example where battery pack 100 is connected to an external device constituted by a laptop computer. However, the external device to which the battery pack of the present invention is connected is not limited to the laptop computer, but may be other electronic devices and electric devices, such as a cellular phone, a portable digital versatile disc (DVD) player, a portable car navigation system, and a portable music player, or an electric tool or an assisted bicycle, for example. In addition, the battery pack may be directly and detachably attached to an external device for use, or may be housed or embedded inside an external device, or may be connected via a cable or the like.

(Housing Case 10)

Battery pack 100 has a box-shaped external appearance extending in one direction as shown in FIGS. 1, 2, 4, and 5, and other figures. A box-shaped main body is constituted by housing case 10, and is divided into two parts, i.e., cover 11 and case body 12, as shown in FIGS. 3, 5, 7, and 9. Housing case 10 includes connector 14, and connection mechanism 13 for connecting to an electric device (a laptop computer herein) corresponding to a driving target to which power is supplied using battery pack 100. Lock mechanism 15 may be further provided to maintain an attached state of battery pack 100 to an electric device. Housing case 10 is made of a material having excellent electrical insulation and thermal insulation properties, such as polycarbonate and other resins.

As shown in FIGS. 3, 5 to 11, a plurality of secondary battery cells 1, circuit board 20, lead plates 21, 22, 25, and others are housed inside housing case 10. According to this example, each of secondary battery cells 1 is constituted by a cylindrical secondary battery cell having a cylindrical exterior can. Secondary battery cells 1 herein are constituted by four secondary battery cells, i.e., first secondary battery cell 1A, second secondary battery cell 1B, third secondary battery cell 1C, and fourth secondary battery cell 1D. Two battery rows, each constituted by two of these cells connected in series, are connected in parallel. A number and a connection form of the secondary battery cells may be freely varied.

Each of secondary battery cells 1 having a cylindrical shape is a lithium ion secondary battery. However, each of the secondary battery cells having a cylindrical shape may be constituted by a chargeable/dischargeable secondary battery such as a nickel metal hydride battery and a nickel-cadmium battery, especially a battery that generates high-temperature heat in a use state.

In addition, secondary battery cells 1A, 1B, 1C, 1D are electrically connected to each other in series or in parallel by lead plates 21, 22, 25. Each of lead plates 21, 22, 25 is produced by bending a metal sheet having excellent conductivity. Lead plates 21, 22, 25 are welded to electrodes on end surfaces of secondary battery cells 1A, 1B, 1C, 1D. Moreover, total + and total − of a battery assembly constituted by secondary battery cells 1A, 1B, 1C, 1D connected to each other are connected to circuit board 20. A charge/discharge circuit and a protection circuit are mounted on circuit board 20. Furthermore, an intermediate potential lead wire for measuring intermediate potential, or potential of a temperature detector for detecting each temperature of secondary battery cells 1 may be connected to circuit board 20 to recognize each voltage of secondary battery cells 1. A thermistor or the like is used as the temperature detector. According to the example of FIG. 11 and other figures, connector 14 is directly connected to circuit board 20, and is disposed in a vertical posture on a side surface side of housing case 10.

(Longitudinal Partition Plate 30)

In addition, as shown in FIG. 11, battery housing spaces 16 are partitioned inside housing case 10 to house secondary battery cells 1. Longitudinal partition plate 30 and lateral partition plates 40 are disposed in housing case 10 to partition battery housing spaces 16. Longitudinal partition plate 30 extends in a longitudinal direction of housing case 10. That is, longitudinal partition plate 30 is disposed substantially parallel to side walls 17 and substantially at a center between side walls 17 to divide an internal space of housing case 10 into two parts. Side walls 17 are located on both sides extending in the longitudinal direction of housing case 10. Longitudinal partition plate 30 is made of a material having excellent electrical insulation and thermal insulation properties, such as mica.

(Lateral Partition Plate 40)

On the other hand, lateral partition plates 40 extend in a lateral direction of housing case 10, that is, substantially parallel to end walls 18 located at both ends of housing case 10 in the longitudinal direction, and are disposed in such positions as to divide the internal space of housing case 10 into three parts in the longitudinal direction of housing case 10 between end walls 18. Each of lateral partition plates 40 is made of a material having excellent electrical insulation and thermal insulation properties. Each of lateral partition plates 40 is preferably made of mica. Mica is highly flame-retardant and non-flammable, has an excellent electrical insulation property, and is relatively inexpensive, and therefore is suitable for a part requiring thermal insulation and electrical insulation properties.

Slits are formed in the respective partition plates to allow longitudinal partition plate 30 lateral partition plates 40 to cross each other in right-angled postures. Longitudinal partition plate 30 has longitudinal side slits 32, while each of lateral partition plates 40 has lateral side slit 42. Each width of the slits is made slightly larger than a thickness of the other partition plate crossing the corresponding slit.

In this manner, the internal space of housing case 10 is divided into six parts as shown in FIGS. 10 and 11 by combining longitudinal partition plate 30 and lateral partition plates 40 to partition battery housing spaces 16 in some of which corresponding secondary battery cell 1 are housed. Secondary battery cells 1 housed in corresponding battery housing spaces 16 formed individually are physically separated from each other. As a result, electrical insulation and thermal insulation between secondary battery cells 1 are achieved.

According to the example described above, one longitudinal partition plate 30 disposed in parallel to the longitudinal direction is used to divide the internal space of housing case 10 into two parts in the lateral direction. However, the present invention is not limited to this configuration. Two or more longitudinal partition plates may be used to divide the internal space of the housing case into three or more parts. Similarly, according to the example described above, two lateral partition plates 40 disposed in parallel to the lateral direction is used to divide the internal space of the housing case into three parts. However, the present invention is not limited to this configuration. One lateral partition plate may be used to divide the internal space of the housing case into two parts, or three or more lateral partition plates may be used to divide the internal space of the housing case into four or more parts.

While the internal space of housing case 10 is divided to form a plurality of battery housing spaces 16, the number of the secondary battery cells is made smaller than the number of battery housing spaces. According to the example of battery pack 100 of the first exemplary embodiment shown in FIGS. 7 and 8 and other figures, the number of secondary battery cells 1 is four even in a state where six battery housing spaces 16 are formed.

Moreover, in the case of the example of battery pack 100 according to the first exemplary embodiment, first secondary battery cell 1A, second secondary battery cell 1B, third secondary battery cell 1C, and fourth secondary battery cells 1D are used as the four secondary battery cells. In this case, battery rows each constituted by two of these cells connected in series are connected to each other in parallel. Specifically, two secondary battery cells, i.e., first secondary battery cell 1A and third secondary battery cell 1C are disposed such that end surfaces of these battery cells face each other to constitute a first battery row, while two secondary battery cells, i.e., second secondary battery cell 1B and fourth secondary battery cell 1D are disposed such that end surfaces of these battery cells face each other to constitute a second battery row. However, a number of series connections need not necessarily be two or more. Each of the battery rows may be constituted by one secondary battery cell and connected to each other in parallel.

(Longitudinal Side Slit 32)

According to the example of FIG. 10, longitudinal side slits 32 are formed at an upper end side of longitudinal partition plate 30, while lateral side slit 42 is formed at a lower end side of each of lateral partition plates 40. In addition, lead slits 31 through which lead plates 22, 25 are inserted are formed in longitudinal partition plate 30 separately from longitudinal side slits 32. Lead slits 31 thus formed are provided on the lower end side of longitudinal partition plate 30. Lead slits 31 and longitudinal side slits 32 are formed at the opposite edges as described above. This configuration eliminates the necessity of work for setting longitudinal partition plate 30 in a state where lead plates 22, 25 and lateral partition plates 40 have been set in housing case 10 in advance. Specifically, this configuration eliminates the necessity for positional alignment to allow simultaneous insertion of lead plates 22, 25 and lateral partition plates 40 into the lead slits and the longitudinal side slits at the time of setting of longitudinal partition plate 30 in housing case 10. Instead, either lead plates 22, 25 or lateral partition plates 40 (for example, only lead plates 22, 25) may be initially guided to lead slit 31 to set longitudinal partition plate 30, and then lateral partition plates 40 may be set to position only lateral side slits 42. Workability improves by dividing the positioning work for the slits in this manner.

Meanwhile, according to the present invention, longitudinal side slits 32 and lateral side slits 42 of longitudinal partition plate 30 and lateral partition plates 40 may be formed in opposite directions. That is, the lead plates may be inserted into longitudinal side slits 32. In this case, the longitudinal side slits are common slits into which the lead plates and the lateral partition plates are both inserted. This configuration prevents formation of an additional gap, thereby improving safety.

Note that a number of lateral partition plates 40 for defining battery housing spaces 16 is adjustable according to required thermal insulation performance. While the number of the plates is one in the example of FIG. 11, the number may be two or more.

(Rib)

A pair of ribs for holding longitudinal partition plate 30 are further formed on the inner surface of housing case 10. Specifically, as shown in a cross-sectional view of FIG. 3, a pair of ribs 34 extending in the longitudinal direction are provided upright on the inner surface of case body 12 of housing case 10 at a substantially central position. Each of ribs 34 is formed integrally with case body 12 and cover 11. A lower end of longitudinal partition plate 30 is inserted between the pair of ribs 34 to hold longitudinal partition plate 30 inside housing case 10.

(Adhesive Material 36)

In addition, an interface between the respective ribs and longitudinal partition plate 30 is filled with flame-retardant adhesive material 36. A gap between the ribs and longitudinal partition plate 30 is filled in this manner to avoid such a situation where flame exhaust possibly produced during thermal runaway of the secondary battery cell reaches the adjacent secondary battery cell.

As described above, longitudinal partition plate 30 is disposed between the side surfaces of the secondary battery cells to prevent damage to the adjacent different secondary battery cell by using longitudinal partition plate 30 even when one of the secondary battery cells causes thermal runaway and blows out flame or high-pressure gas toward the side surface. On the other hand, in a battery pack according to Comparative Example 1 shown in a cross-sectional view of FIG. 12, flame is considered to leak toward an adjacent secondary battery cell through gap 35Y when gap 35Y is present at a connecting portion between ribs 34Y and longitudinal partition plate 30Y.

Therefore, as shown in a cross-sectional view of FIG. 3, a gap between ribs 34 and the lower end of longitudinal partition plate 30, and an upper end of longitudinal partition plate 30 are filled with flame-retardant adhesive material 36 to fill the gap. This configuration reduces the gap between ribs 34 and longitudinal partition plate 30, thereby preventing formation of a path for flame exhaust or the like. Flame-retardant adhesive material 36 may be made of silicone resin or the like. A temporary sealing effect is produced by filling the gap with adhesive material 36 thus provided. In particular, blowout of flame and high-pressure gas generally continues for a short period of approximately a few seconds. In this case, direct exposure of the adjacent secondary battery cell to flame or high-pressure gas is avoidable if strength of the flame or the high-pressure gas is reduced. Accordingly, sufficient fire spread preventing effect is expected to be achieved.

(Insulating Thermal Resistant Plate 2)

In addition, the side surface of each of the secondary battery cells is covered with insulating thermal resistant plate 2. Insulating thermal resistant plates 2 are provided so as to cover at least opposing regions of respective side faces of secondary battery cells 1 disposed adjacent to each other such that these side faces face each other. Each of insulating thermal resistant plates 2 is curved along the side surface of corresponding secondary battery cell 1. According to this configuration, each of insulating thermal resistant plates 2 is capable of covering corresponding secondary battery cell 2 along the side surface in a posture easily coming into close contact with the side surface, thereby efficiently improving a thermal insulation property in a limited space.

When flame is exhausted from the side surface in a state where the secondary battery cells are disposed in parallel, the flame is considered to flow into adjacent secondary battery cell 1 through a gap between longitudinal partition plate 30Z and housing case 10Z in a battery pack according to Comparative Example 2 shown in a cross-sectional view of FIG. 13A. An exhausting path is considered to be formed as a route through which flame leaks through a gap between housing case 10Z and longitudinal partition plate 30Z in areas above and below longitudinal partition plate 30Z, depending on a flame exhaust position.

On the other hand, in a configuration where insulating thermal resistant plate 2 which is curved as shown in FIG. 13B is provided, flame exhaust possibly caused is not directed toward adjacent secondary battery cell 1, but toward the opposite side in the housing case 10 by curved insulating thermal resistant plate 2. This configuration prevents direct exposure of adjacent secondary battery cell 1 to high-temperature flame or gas, thereby preventing fire spread or fire catch.

Each of insulating thermal resistant plates 2 shown in FIG. 3 and other figures is curved in a U shape around a position where a pair of secondary battery cells 1 come closest to each other in a cross-sectional view. In this case, a flame exhaust direction can be regulated such that flame exhaust caused by secondary battery cell 1 flows not toward the side surface but toward a rear side in an up-down direction. Accordingly, safety improves.

In addition, each of insulating thermal resistant plates 2 may contain a fibrous material. Moreover, each of insulating thermal resistant plates 2 is constituted by a plate member made of an inorganic material. It is preferable that each of insulating thermal resistant plates 2 is made of mica. This configuration achieves high thermal resistance at low cost.

(Thermal Insulator 50)

In addition, longitudinal partition plate 30 constitutes thermal insulator 50. According to the example shown in the cross-sectional views of FIG. 3 and FIG. 14, first thermal insulator 51 is provided on a side facing a side surface of the cylindrical shape of first secondary battery cell 1A on the right side, and projects to come into contact with this side surface of the cylindrical shape. In addition, second thermal insulator 52 is provided on a side facing a side surface of a cylindrical shape of second secondary battery cell 1B on the left side, and projects to come into contact with this side surface of the cylindrical shape. This configuration brings a partially projected portion of longitudinal partition plate 30 into contact with the side surface of the cylindrical shape of the secondary battery cell, thereby separating longitudinal partition plate 30 from the secondary battery cell to form an air layer which improves a thermal insulation property.

When thermal runaway is caused by one of secondary battery cells 1 disposed in parallel to each other inside housing case 10 such that the side surfaces of the cylindrical shapes are adjacent to each other, heat is considered to be transferred via longitudinal partition plate 30′ interposed between adjoining secondary battery cells 1 in a battery pack according to Comparative Example 3 shown in FIG. 15. For preventing this situation, methods such as use of a longitudinal partition plate made of a material having higher thermal insulation performance, and a thickness increase are considered to be adopted. However, the material change or the film thickness increase may raise costs. Particularly, the film thickness increase raises a weight of the longitudinal partition plate and therefore is not preferable for the battery pack for which size and weight reduction are demanded.

Therefore, as shown in FIG. 14, battery pack 100 according to the first exemplary embodiment includes thermal insulator 50 partially projected from both surfaces of longitudinal partition plate 30. This thermal insulator is disposed at a position in contact with a vicinity of a top of the side surface of the cylindrical shape of secondary battery cell 1 to make distance D12 between the secondary battery cells longer than distance D11 the secondary battery cells of a configuration including no thermal insulator as shown in FIG. 15. The air layer between the secondary battery cells enlarges by separation between the secondary battery cells. Accordingly, the enlarged air layer functions as a thermal insulating layer, thereby improving the thermal insulating effect between the secondary battery cells. Moreover, this configuration allows reduction of the thickness of the longitudinal partition plate itself, thereby contributing to weight reduction of the entire battery pack.

Thermal insulator 50 may be formed integrally with longitudinal partition plate 30, but is preferably a member separated from longitudinal partition plate 30. In this case, a material different from the material of the longitudinal partition plate is available to constitute the thermal insulator. Thermal insulator 50 is therefore allowed to be made of a material having a higher thermal insulation property than the material of longitudinal partition plate 30. Accordingly, reduction of cost and weight is achievable by providing a member exhibiting higher heat insulation not on the entire surface of longitudinal partition plate 30 but on a part of the surface. As described above, mica is preferably used as the material of thermal insulator 50 having an excellent thermal insulation property. In addition, when thermal insulator 50 is a member separated from longitudinal partition plate 30, the thermal insulator is bonded to the surface of longitudinal partition plate 30. A double-sided tape or an adhesive is used for this bonding.

Note that thermal insulator 50 may be extended in the longitudinal direction of longitudinal partition plate 30, or may be partially cut off in the longitudinal direction. In the example of FIG. 10 and other figures, thermal insulator 50 is cut off at the portions where the longitudinal side slits 32 are formed. In addition, the thermal insulator may be extended in a slit shape as described above, or may be parts having rectangular shapes and provided separately from each other. Even when the thermal insulator is partially provided in the longitudinal direction, the thermal insulator is capable of forming a thermal insulating layer by coming into contact with the side surface of the cylindrical secondary battery cell in contact with the thermal insulator. Moreover, the volume of the thermal insulator to be used decreases, wherefore reduction of cost and weight is achievable.

In addition, first thermal insulator 51 and second thermal insulator 52 may be disposed such that centers of respective insulators 51 and 52 are shifted from each other in a left-right direction of longitudinal partition plate 30 in the cross-sectional view as shown in FIG. 14. By shifting centers of the cross sections of left and right secondary battery cells 1 from each other in the manner described above, positions of stresses applied when secondary battery cells 1 are pressed are shifted from each other in the left-right direction of longitudinal partition plate 30. Accordingly, concentration of the stresses is reduced. Moreover, while shifting the centers of the cross sections of secondary battery cells 1 from each other in the cross-sectional view, first thermal insulator 51 and second thermal insulator 52 are preferably arranged so as to partially overlap with each other in the left-right direction of longitudinal partition plate 30. In this manner, mechanical rigidity increases.

(Heat Absorber 60)

Thermal runaway is reduced by disposing heat absorbers 60 inside the housing case. In this manner, each of heat absorbers 60 absorbs heat generated by the secondary battery cell causing thermal runaway in a case of thermal runaway caused by any one of the secondary battery cells inside the housing case, thereby reducing a chain of thermal runaway to the adjacent secondary battery cell. The number of battery housing spaces 16 is larger than the number of the secondary battery cells. In this case, heat absorbers 60 are allowed to be disposed in the battery housing spaces where the secondary battery cells are not housed. Accordingly, efficient disposition of heat absorbers 60 is achievable inside the housing case having a limited volume without the necessity of preparing a space dedicated for heat absorbers 60.

Each of heat absorbers 60 is a metal part having a cylindrical shape which is hollow inside. This shape increases a surface area and enhances a heat absorption effect while reducing a weight of heat absorber 60. An aluminum pipe can be preferably used as heat absorber 60 made of metal. Aluminum has stable characteristics such as lightweight, high heat transfer property, low-cost, and no corrosion.

In addition, heat absorber 60 is not necessarily required to have the same length as the length of the secondary battery cell, and may be shorter than the length of the secondary battery cell. This reduction of the length can reduce material cost and weight. The length of heat absorber 60 is appropriately set according to a required amount of heat absorption such as the capacity of the secondary battery cell to be used and the temperature at the time of heat generation.

When heat absorbing body 60 is shortened, heat absorber 60 is fixed without movement in corresponding battery housing space 16. For example, double-sided tape or adhesive is used. When heat absorber 60 is made shorter than the secondary battery cell, heat absorber 60 is eccentrically fixed in battery housing space 16 in such a manner as to come close to different battery housing space 16 which is located adjacent to corresponding battery housing space 16 in the longitudinal direction, and houses the different secondary battery cell. By disposing heat absorber 60 close to the end surface of the secondary battery cell corresponding to a heat absorbing target, the heat absorbing effect can be effectively exerted during heat generation from the corresponding secondary battery cell.

INDUSTRIAL APPLICABILITY

The battery pack according to the present invention is suitably applicable to a chargeable/dischargeable battery pack for a battery-driven device such as a laptop computer, a cellular phone, a portable digital versatile disc (DVD) player, a portable car navigation system, a portable music player, a power tool, and an assisted bicycle. 

The invention claimed is:
 1. A battery pack comprising: a plurality of secondary battery cells connected to each other in series and/or in parallel; and a housing case that includes a plurality of battery housing spaces, wherein each of the plurality of secondary battery cells is housed in a corresponding one of the plurality of battery housing spaces, a number of the plurality of battery housing spaces is larger than a number of the plurality of secondary battery cells, a heat absorber is disposed in one of the plurality of battery housing spaces, the one of the plurality of battery housing spaces housing none of the plurality of secondary battery cells, the plurality of battery housing spaces are defined by a longitudinal partition plate that extends in a longitudinal direction of the housing case, and lateral partition plates including a first lateral partition plate and a second lateral partition plate, each of which extends in a lateral direction orthogonal to the longitudinal direction of the housing case, the plurality of secondary battery cells are arranged such that end surfaces of adjacent ones of the plurality of secondary battery cells face each other via the first lateral partition plate interposed therebetween in a longitudinal direction of the plurality of battery housing spaces, and side surfaces of adjacent ones of the plurality of secondary battery cells face each other via the longitudinal partition plate interposed therebetween, and the heat absorber is disposed adjacent to an end surface of one of the plurality of secondary battery cells, wherein the heat absorber faces the end surface of the one of the plurality of secondary battery cells via the second lateral partition plate interposed therebetween.
 2. The battery pack according to claim 1, wherein each of the plurality of secondary battery cells has a cylindrical exterior can.
 3. The battery pack according to claim 2, wherein the heat absorber is a metal part that has a columnar shape that is hollow inside.
 4. The battery pack according to claim 1, wherein the heat absorber has a length smaller than a length of each of the plurality of secondary battery cells.
 5. The battery pack according to claim 1, wherein the heat absorber is made of aluminum.
 6. The battery pack according to claim 1, wherein side surfaces of the plurality of secondary battery cells, including the side surfaces of the adjacent ones of the plurality of secondary battery cells, are covered by insulating thermal resistant plates, and each of the insulating thermal resistant plates is made of mica.
 7. The battery pack according to claim 1, wherein the heat absorber is shorter than the one of the plurality of battery housing spaces in the longitudinal direction of the plurality of battery housing spaces, and is asymmetrically positioned relative to a longitudinal center of the one of the plurality of battery housing spaces. 